In the production of coke, the scheduling of the pushing cycles of the coke ovens generally is determined according to the techniques hereinafter described.
The operator begins with a known total number of tons of coke required of the battery per day. Knowing the number of ovens being operated and the total tons of coke produced per oven, per push, the operator determines the aim coke cycle for each oven. Such coke cycle is typically in the range of 18-20 hours for each oven.
Therefore, the operator knows, for a given charge time, that the oven must have a push time a pre-selected number of hours thereafter. With batteries having a large number of ovens, typically 80, very little deviation can be permitted from this pre-selected push time, or else the deviations of all ovens, which are additive, will cause the battery to become severely out of scheduling control. Skilled coke oven operators consider a permitted push time deviation of plus or minus 1/4 hour as a practical optimum.
As is known in the art, each coke cycle includes: (1) a charge time, (2) a devolatilizing period immediately following the charge time, (3) a soaking period immediately following the devolatilizing period, and (4) a push time immediately following the soaking period.
For the purpose of this invention, the charge time will be deemed to have occurred upon completion of charging and leveling of coal within the oven.
As is well known, the devolatilizing period of a coke cycle is the period when the volatile constituents of the crushed coal in the oven are vaporized by reason of the heating of the oven. Such volatile by-products are withdrawn from the oven for conventional treatment. For the purposes of this invention, the term volatiles means those volatiles which are readily condensed into a liquid catch medium as disclosed hereinafter.
The length of the devolatilizing period for a given coal mix is a variable that the operator can change, and it depends upon the heating practice used on the oven, i.e., the firing rate of fuel, the reversal cycle on the oven, and the given coal mix.
The coke soaking period takes place upon completion of the devolatilizing period. The purpose of the coke soaking period is to heat the coke, in order to impart the desired physical properties to the finished product. Such properties include coke stability and hardness, as described in ASTM Test Method D-3402. A soaking period which is too short results in coke having low stability. Conversely, a too long soaking period results in the coke cycle being too long, and also is wasteful of heat. For a given coal mix, the operator determines from past experience how long a soaking period should be used to achieve optimum coke properties.
Therefore, in operating a coke oven battery to achieve a given output, with good quality coke, the operator must operate each oven over a coke cycle that has certain generally fixed parameters. These fixed parameters include:
(1) the aim total coke cycle time of the oven, i.e., the time between charge and push (plus or minus permitted deviation), and PA0 (2) the total coke soaking time.
In order to change the length of coke cycle time for the purpose of scheduling battery production rate, the only significant variable in the coke cycle available to the operator for flexibility is the length of devolatilizing period. Since the coke soaking period can only begin upon completion of the devolatilizing period, it is critical for the operator to be able to tell when the devolatilizing period ends.
By being able to determine the length of the devolatilizing period for a given coke oven, with a given coal charge, and a given heating practice, the operator can add the pre-selected soaking period, and arrive at a total coke cycle time that can be compared with the aim coke cycle time, and if such coke cycle times are significantly different, the operator can adjust the heating rate of the oven in subsequent coke cycles. If resulting coke properties indicate that the soaking period was too short, this tells the operator that the devolatilizing period in subsequent cycles should be shortened (without changing the fixed, aim push time outside the permitted deviation) by adjustment of the heating rate, in order to lengthen the coke soaking period.
On the other hand, if experience indicates a too long soaking time, this tells the operator that the devolatilizing period must be lengthened (without changing the fixed, aim push time outside the permitted deviation) by adjustment of the heating rate, in order to begin the soaking period later in the cycle.
There is a need, therefore, for a method of determining when the end of devolatilizing occurs, and for adjusting coke oven heating using this information to provide a coke cycle which (1) meets the aim push time within permitted tolerance, and (2) at the same time provides a coke soaking period of pre-selected length.
The method of this invention satisfies such need.